Phases of the Moon

4th Grade Science

Our Moon

The regular daily and monthly rhythms of Earth's only natural satellite, the moon, have guided timekeepers for thousands of years. Its influence on Earth's cycles, notably tides, has been charted by many cultures in many ages. The moon moderates Earth's wobble on its axis, leading to a relatively stable climate over billions of years. From Earth, we always see the same face of the moon because the moon is spinning on its axis at the same speed that it is going around Earth (that is, it is in synchronous rotation with Earth).

Phases of the Moon (and other cool facts)

  • the Moon was probably made 4.5 billion years ago when a large object hit the Earth and blasted out rocks that came together to orbit round the Earth. They eventually melted together, cooled down and became the Moon. For another 500 million years pieces of rock kept striking aginst the surface of the Moon.

  • You can see the surface of the Moon by using a pair of binoculars or a small telescope. The Moon’s surface shows the damage caused by these large pieces of rock hitting it billions of years ago. The surface is covered in craters, pits and scars.

  • From the Earth we can only see one side of the Moon; the other side is always turned away from us. Photographs from space show a similar scarred surface on the other side.

  • The Earth has a much greater surface than the Moon and was also hit by debris (the rocks from explosions and collisions) but over time the damage has disappeared. The wind and rain in the Earth’s atmosphere has helped to erode the pits and craters.

  • The Moon has no atmosphere and so we can still see the damage caused billions of years ago.

  • If you look at the Moon when it is nearly full you can see the dark areas which are known as the seas. (They are all given Latin names, such as Mare Serenitatis – the Sea of Serenity, or Mare Frigoris – the Sea of Cold).These are not really seas but are huge expanses of smooth dark lava.

Figure 1. A map of the Moon.

  • All parts of the Moon are lit in turn by the Sun. As it rotates round the Earth we see different fractions of the sunlit half, or hemisphere, of the Moon. These are known as the phases of the Moon, or lunar phases. The Moon changes from a thin crescent to a full moon and back again to a crescent in one month (actually 29 days, which is a lunar month).

Figure 2. The Phases of the Moon.

  • This diagram shows the phases of the moon, from a new moon, which you can hardly see at all, round to a full moon and back again in just over four weeks. Follow the phases in an anticlockwise direction(the opposite way from how the hands of a clock move).

  • The waxing Moon. “Waxing” means growing. After the new moon appears in the sky as a tiny sliver of light the moon waxes. It grows into a crescent, curving to your left as you look at it and then into a half moon. This takes a week and so the period is described as the Moon’s first quarter.

  • The waxing gibbous Moon. Gibbous means humped and describes the shape of the Moon as it grows from a half moon to a full moon. Another week has passed and this is the Moon’s second quarter.

  • The waning Moon. “Waning” means shrinking. Now the Moon begins to get smaller again – it “wanes”. The third quarter takes us from a full moon to a half moon again, but this time it is the right hand side of the moon that shines.

  • The waning crescent Moon. The last quarter takes us from a half moon back to a crescent moon, facing right, and to a point where the moon disappears.

  • When the Moon is a crescent and only the crescent is being illuminated by the Sun, you can often see the shadow of the rest of the Moon. This is caused by reflection of sunlight from the Earth. It is sometimes called “the old moon in the new moon’s arms”.

Figure 3. The effect of earth shine on the moon.

  • The gravity of the Moon, the pull which it exerts on the Earth, causes two high tides on the Earth every day – one every 12 hours and 25 minutes.

  • The first man to make proper maps of the moon was Galileo. Galileo did not invent the telescope but by 1609 he had developed a telescope that could magnify objects to 20 times, and with this telescope he began his careful study of the Moon’s surface.

  • The first person to walk on the Moon was the American astronaut, Neil Armstrong, who stepped out of his space landing craft, the Eagle, on 21 July 1969 with these famous words, “That’s one small step for man, one giant leap for mankind”.

Figure 4. A photograph of the Earth taken from the surface of the Moon.

  • The Moon is 239,000 miles, or 384,000 kilometres away from the Earth.

  • The Moon is much smaller than the Earth, with a diameter of 2159 miles, or 3476 kilometres. It is airless, waterless and lifeless.

What are the Phases of the Moon?

It takes our Moon about 29.5 days to completely cycle through all eight phases. Occasionally (about every 2.7 years) there are two Full Moons in the same month. This is referred to as a Blue Moon. Hence the saying "Once in a Blue Moon".

New Moon

The side of the moon facing the Earth is not illuminated. Additionally, the moon is up through out the day, and down through out the night. For these reasons we can not see the moon during this phase.

Waxing Crescent

During this phase, part of the Moon is beginning to show. This lunar sliver can be seen each evening for a few minutes just after sunset. We say that the Moon is "waxing" because each night a little bit more is visible for a little bit longer.

First Quarter

During first quarter, 1/2 of the moon is visible for the first half of the evening, and then goes down, leaving the sky very dark.

Waxing Gibbous

When most of the Moon is visible we say it is a Gibbous Moon. Observers can see all but a little sliver of the moon. During this phase, the Moon remains in the sky most of the night.

Full Moon

When we can observe the entire face of the moon, we call it a Full Moon. A full moon will rise just as the evening begins, and will set about the time morning is ushered in.

Waning Gibbous

Like the Waxing Gibbous Moon, during this phase, we can see all but a sliver of the Moon. The difference is that instead of seeing more of the Moon each night, we begin to see less and less of the Moon each night. This is what the word "waning" means.

Last Quarter

During a Last Quarter Moon we can see exactly 1/2 of the Moon's lighted surface.

Waning Crescent

Finally, during a Waning Crescent Moon, observers on Earth can only see a small sliver of the Moon, and only just before morning. Each night less of the Moon is visible for less time.


Keep track of the moon each night for four weeks. Draw a picture to represent what you see in the sky each night on the calendar.
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Flocabulary - Moon Phases